Traditionally, disposable absorbent articles, such as infant diapers or training pants, adult incontinence products and other such products, are constructed with a moisture-impervious outer backing sheet (or “backsheet”), a moisture-pervious body-contacting inner liner sheet (or “topsheet”), and a moisture-absorbent core (or “absorbent core”) sandwiched between the liner sheet and the backing sheets. These disposable absorbent articles oftentimes include additional features such as elastic waist bands, elastic leg bands, and stretchable side panels. Further, decorative graphics can be incorporated into the disposable absorbent article for aesthetic and functional purposes.
Disposable absorbent articles are generally assembled on an automated production line by separately supplying the individual components of the absorbent article to the production line at predetermined locations along the machine direction, and layering the individual components to form an integrated absorbent article. Various methods are available for bringing these individual components together so that the components in the integrated product are in a desired relation with respect to each other. In bringing these individual components together, various known methods have been used to sense the position of a particular component, and then to adjust the placement of subsequent components in order to properly position them with respect to the previously sensed component.
Prior art methods for assembling components of absorbent articles have employed photo/optical techniques to sense reference markers on the individual components. The reference markers assist in cutting and placing the individual components onto the integrated absorbent article. The reference markers have typically been included in the final assembled product. This is so because the reference markers employed in prior techniques need to be sensed downstream in the production line to provide error correction, requiring complex feed-back control systems. However, the inclusion of the reference markers on the final assembled product can detract from the aesthetics of the product and are therefore not desirable. These methods have, in particular, been used to incorporate decorative graphics into absorbent garments.
For example, U.S. Pat. No. 5,286,543 (“the '543 patent”), U.S. Pat. Nos. 5,235,515 and 5,286,543 to Ungpiyakul et al. disclose a system for selectively providing predetermined segments of web material to an absorbent article production line using a reference marker that is incorporated into the final assembled absorbent article. The predetermined segments of web material comprise discrete graphic patches corresponding to the tape landing zone of the diaper that are provided on a continuous, pre-printed roll. Each patch is said to have a predetermined set of graphics that are “congruously entire.” The patches are also said to abruptly change from graphics set to graphics set and, therefore, from diaper to diaper because there is no modulating transition between the adjacent compositions formed on the original supply roll of web material. The patches are said to be provided with reference markers delineating the boundaries between individual web or patch segments. The reference markers comprise any signaling mechanism that is recognizable by a machine.
During the production of the absorbent article according to the '543 patent, a first sensing means detects the reference marker associated with the graphic as the web containing the graphics is unwound. Then, at a remote position in the manufacturing process, a second sensor observes the portions of the reference markers that remain permanently attached to each web segment. If the web segment is not correctly cut, the remote, second sensor detects this improper separation of the graphic and corrects for any improper cutting of the web segment by generating an updated set reference value based on where the remote, second sensor observes the reference marker downstream in the manufacturing line. The system is then selectively adjusted to incorporate the updated set reference value to assure that subsequent patches of web material are properly cut and positioned with respect to the other components forming the absorbent article.
The '543 patent at col. 14, lines 24–55 admits to be distinguishable from so-called “conventional techniques” employing, for example, a “shift register” scheme, for matching detector information to a particular manufacturing operation, such as the operation of a cutter. The so-called conventional techniques are said not to be capable of withstanding severe process disturbances. These disturbances, described as start-ups, splices within various web materials, and non-uniform stretching of web material caused by a non-uniform winding of the web materials onto the associated supply roll, are said to cause an improper placement of a significant number of patches and thereby increase cost and waste.
To overcome process disturbances, the so-called conventional techniques discussed in the '543 patent are said to be sensitive to the distance between the sensing means for detecting the reference marker and the cutting mechanism. In other words, the reference marker sensor in the conventional techniques had to be placed relatively close to the cutting mechanism because, if for example, a detector is mounted a relatively large distance, such as 25 web segment lengths before the cutting unit, the phasing mechanism can phase 25 patches too soon. Where a new roll of material is spliced onto an expiring roll with the sets of patch graphics on the new roll being “out of phase” from the previous roll, up to 25 patches may be cut incorrectly. Furthermore, the '543 patent states that in conventional techniques in which the detector is mounted a large distance from the cutter, the individual sets of print design graphics may not be exactly equally spaced, and the relative position of the patch graphics measured at the detector may not accurately represent the relative position of the patch graphics when the web material reaches the cutting mechanism. Due to this, the '543 patent recognizes that the greater the distance between the detector and the cutting mechanism, the larger the errors can be.
To eliminate these processing errors in the situation where the sensor and the cutting mechanism are remote from one another, the '543 patent employs feedback control in a manner where the reference marker (i) is not removed following its initial sensing by the first sensor, and (ii) is applied to the final assembled absorbent article for subsequent reading by the second, remote sensor. Consequently, the reference marker in the '543 patent, by virtue of being on the final absorbent article, is constructed to provide for a selected separating of discrete graphics. Indeed, without the reference marker on the final absorbent article in the '543 patent, feedback control is effectively eliminated from the system described in the '543 patent, and concomitantly process disturbances evidently will be permitted to cause the improper cutting and/or placement of the graphic, leading to a graphic that is neither aesthetically pleasing nor congruously entire.
Thus, the reference marker portions that remain upon each patch of web material in the final article of the '543 patent are “constructed to provide for a selected separating” of the graphic sets by enabling both the upstream first sensor and the downstream second sensor to detect the location of the reference marker portion and thereby register and control the location and cutting of the predetermined graphic sets. A claimed aspect of the invention of the '543 patent is the use of the reference marker portions to provide for the “selected separating” of the graphic sets. This “selected separating” employs an automated registration and “set point error” correction control loop using feedback from the second sensor. The second sensor detects the reference marker portions located on the patches of web material to enable the feedback control and thereby “provide for a selected separating” of the graphic sets.
But even though the so-called conventional techniques described in the '543 patent do not employ the reference marker later in the process line, they still apparently leave the reference marker on the final, assembled absorbent article. As noted previously, the reference markers in some instances are aesthetically displeasing, so leaving them on the final assembled absorbent article can detract from the presentation of the article.
Similarly, U.S. Pat. No. 5,766,389 to Brandon et al. discloses a process for controllably registering a plurality of components of a continuously moving first layer with a plurality of reference marks on a continuously moving second layer with pre-printed graphics. Brandon's registration process comprises the steps of (1) providing a continuously moving first layer having a plurality of components thereon, (2) providing a continuously moving second layer having a plurality of reference marks thereon, (3) sensing the distance between two successive reference marks, (4) generating a signal in response to the sensed distance, (5) adjusting the distance between subsequent successive reference marks to a selected distance, (6) joining the continuously moving first and second layers together, (7) sensing the position of each reference mark relative to its associated component, (8) generating a signal when one of the reference marks is out of position relative to its component, (9) processing the signal in accordance with preprogrammed instructions to generate a speed command signal, and (10) adjusting the speed of the continuously moving second layer in response to the speed command signal in accordance with preprogrammed instructions.
According to these prior methods, the assembled absorbent article must contain the sensed reference marker(s) to properly enable the complex feed-back control systems of the registration process. The inclusion of the reference marker(s) in the assembled product can detract from the aesthetic qualities of the final absorbent article, and the feed-back control can overly complicate the production line. For example, Procter & Gamble's Pampers™ Baby-Dry™ (tape closure system) and Pampers™ Rash Guard™ (hook and loop closure system) diapers include a reference marker on the closure landing systems, which apparently assists in cutting and placing the graphic on the assembled absorbent article. This marker is visibly apparent in the final assembled product, and detracts from the graphic on the tape landing zone. Further, the assembly and layering of the component parts in the machine direction, as shown in the prior art, limits the flexibility of the production line to incorporate a variety of different graphics into the integrated absorbent article.
In addition to the shortcomings described above, the prior art attempts at placing decorative graphics on absorbent garments are both expensive and, because of their complexity, sensitive to equipment and programming failures. These and other disadvantageous features of the prior art are overcome by the invention according to the preferred embodiments.